Shock absorber and compression valve assembly

ABSTRACT

In combination in a shock absorber, a pressure cylinder, a piston movable within the cylinder, valve means on the piston for controlling the flow of fluid through the piston between the opposite sides thereof, a fluid reservoir adjacent the cylinder, and a compression valve assembly for communicating fluid between the reservoir and the cylinder, the compression valve assembly comprising a first member defining a first flow passage and a first valve seat, a second member defining a second flow passage and a second valve seat, and at least one generally ring-shaped valve element interposed between the first and second members and adapted for free longitudinal sliding movement toward and away from engagement with the first and second valve seats.

United States Patent Palmer Sept. 11, 1973 1 SHOCK ABSORBER ANDCOMPRESSION VALVE ASSEMBLY [75] Dale A. Palmer, Monroe, Mich.

Inventor:

Monroe Auto Equipment Co., Monroe, Mich.

Filed: July 29, 1971 Appl. No.: 167,135

Related US. Application Data Continuation-impart of Ser. No. 867,427,Sept. 17, 1968.

Assignee:

US. Cl. 188/322, 137/493.9 Int. Cl F16f 9/34 Field of Search 188/282,317, 320,

References Cited UNITED STATES PATENTS 3,194,262 7/1965 Hamilton et al.137/493 2,849,090 8/1958 De Koning et al 137/4938 FOREIGN PATENTS ORAPPLICATIONS 1,058,601 11/1953 France 188/320 Primary Exqminer George E.Halvosa Attorney-J. King Harness, H. Keith Miller et al.

[ 5 7 ABSTRACT In combination in a shock absorber, a pressure cylinder,a piston movable within the cylinder, valve means on the piston forcontrolling the flow of fluid through the piston between the oppositesides thereof, a fluid reservoir adjacent the cylinder, and acompression valve assembly for communicating fluid between the reservoirand the cylinder, the compression valve assembly comprising a firstmember defining a first flow passage and a first valve seat, a secondmember defining a second flow passage and a second valve seat, and atleast one generally ring-shaped valve element interposed between thefirst and second members and adapted for free longitudinal slidingmovement toward and away from engagement with the first and second valveseats.

6 Claims, 10 Drawing Figures .PATENTED SEP] 1 I973 sum 1 or 2 RELATEDAPPLICATIONS This is a continuation-in-part application of US.application, Ser. No. 867,427, filed Sept. 17, 1969, now abandoned.

- SUMMARY OF THE INVENTION The present invention relates generally tohydraulic shock absorbers and more specifically to a new .and improvedcompression valve assembly which functions to selectively communicatehydraulic fluid between a fluid reservoir and a pressure cylinder withinwhich the shock absorber piston and piston rod are reciprocallydisposed. The new and improved compression valve assembly of the presentinvention is of an extremely simple' and compact design and features avalve arrangement which permits interchanging of valve elements tocontrol the compression characteristics of the assembly, therebyproviding for universality of application.

The valve arrangement is designed such that one or more valve elementsare utilized for controlling the compression characteristics of astandard shock absorber unit, and wherein the total number and/orthickness of the valve elements may be varied, i.e., increased ordecreased, to change the compression characteristics of the shockabsorber. Another feature of the compression valve assembly of thepresent invention resides in the fact that the aforesaid valve elementsare free to move toward and away from associated valve seats, therebyobviating the need for any clamping means or the like heretoforecommonly used in similar type'valve assemblies. This, of course, reducesthe number of component parts of the assembly and the attendantmanufacturing costs thereof. I i v 1 It is accordingly a general objectof the present invention to provide a new and improved compression valveassembly for hydraulic shock absorbers and the like.

It is a more particular object of the present invention to provide a newand improved compression valve assembly of the above character whosecompression characteristics may be easily changed.

It is another object of the present invention to provide a new andimproved compression valve assembly which utilizes one or more generallyring-shaped valve elements, the total number of which elements and/orthicknesses thereof being variable to control the compressioncharacteristics of the assembly.

It is a further object of the present invention to provide a compressionvalve assembly of the above described type which obviates the need forany clamping or other fixedly mounting means for the valve elements.

It is yet another object of the present invention to provide acompression valve assembly of the above described type which utilizes avalve plate having a generally axially extending guide'portion uponwhich the valve elements are slidably mounted and guided for movementtoward and away from associated valve seats.

bly which is of an extremely simple design, is easy to assemble andeconomical to commercially manufacture.

Other objects and advantages of the present invention will becomeapparent from the following detailed description taken in conjunctionwith the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a longitudinal sideelevational view, partially broken away, of a shock absorber embodyingthe principles of the present invention;

FIG. 2 is an enlarged fragmentary cross sectional view of a portion ofthe compression valve assembly incorporated in the shock absorber shownin FIG. 1;

FIG. 3 is an exploded assembly view of the compression valve assemblyshown in FIG. 2;

FIG. 4 is a fragmentary cross sectional view taken substantially alongthe line 44 of FIG. 5;

FIG. 5 is an enlarged side elevational view, partially broken away, ofthe compression valve assembly shown in FIG. 2, as seen during acompression phase of the associated shock absorber unit;

FIG. 6 is a view similar to FIG. 5 showing the compression valveassembly during the rebound phase of the associated shock absorber unit;

FIG. 7 is a transverse cross sectional view of a compression valveassembly in accordance with an alternate embodiment of the presentinvention;

FIG. 8 is a view of the modified valve assembly similar to FIG. 7 andillustrates the valve member therein in a partially closedconfiguration; I

FIG. 9 is a view similar to FIGS. 7 and 8 and illus trates the valvemember of the valve assembly in a substantially open configuration; and

FIG. 10 is a transverse cross sectional view taken substantially alongthe line l0l0 of FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION Referring now in detail to thedrawing and in particular to FIG. 1, a shock absorber assembly 10, inaccordancewith a preferred embodiment of the present invention, is shownas comprising upper and lower, generally tubular-shaped, concentricallyand telescopically oriented members 12 and l4, As is conventional, themembers l2, 14 are longitudinally movable relative to one another andare adapted for operative attachment to the sprung and unsp'rungportions of an associated vehicle or the like. The upper end of themember 12 is provided with a generally cup shaped end cap member 16which is fixedly'secured to the member 12 and is provided with anupwardly extending, externallythreaded stud-like mounting member 18adapted to be secured by any suitable means to one of the associatedvehicle portions. The lower end of the member 14 is provided with asimilar type, generallycup-shaped end cap member 20 which is fixedlysecured to the member 14 and is provided with a ring-like attachingelement 22. The opposite (upper) end of the member 14 is provided withan end cap member 24 which is formed with a central aperture 25 and withthe member 14 defines a fluid reservoir 26. A longitudinally disposedpiston rod '30 extends axially of the assembly 10 and has the upper endthereof projecting through the aperture 25.

Disposed concentrically within the reservoir 26 is a longitudinallyextending pressure cylinder 32, the upper end of which is provided witha piston rodguide member 34 having a downwardly extending, reduceddiameter portion 36 adapted to be received within the upper end of thecylinder 32. The guide member 34 defines a central annular bore 38through which the pis-' ton rod 30 extends. A rubber or other suitablesealing element 40 surrounds the piston rod 30 and is confined withinthe interior of the cap member 24 by a suitable retainer member 42 andhelical coil spring 44. A helical baffle 45 is disposed within thereservoir 26 interjacent Y the outer periphery of the cylinder 32 andthe inner periphery of the member 14 and serves to reduce the turbulanceof hydraulic fluid or the like as the same moves into and out of thereservoir 26, as is well known in the I art.

A piston member, generally designated 46, is mounted on a lower, reduceddiameter end portion 48 of the piston rod 30 and is adapted to besecured thereon by a suitable threadably mounted retaining nut 50. Thepiston member 46 is provided with a plurality of circumferentiallyspaced radially outermost disposed set of longitudinally extendingapertures 52 which are located between a pair of radially spaced,concentric valve seats 54 and 56 provided on the upper end of the member46. The valve seats 54, 56 are cooperable with and adapted to be engagedby a relatively thin, washerlike valve 58 which functions to close theapertures 52 when the piston rod 30 is moved upwardly within thepressure cylinder 32. A spring disk 60 is disposed directly above thevalve 58 and is adapted to resiliently urge the latter toward the valveseat 54, 56. A retaining member 62 having a plurality of apertures 64therein is disposed directly above the spring disk 60 and bears againsta radially extending shoulder 66 formed adjacent the end of the pistonrod portion 48. An annular valve seat 68 is provided on the lower sideof the piston member 46 at a position radially outwardly of a pluralityof circumferentially spaced, longitudinally extending inner set ofapertures 69 and is adapted to be engaged by a thin washer-like valve 70which is vurged against the valve seat 68 by means of an annular sleevemember 72 which is slidable downwardly along the nut 50 and is adaptedto be resiliently urged upwardly by a helical coil spring 74, the lowerend of which bears against a radially outwardly extending flange portion76 formed on the lower end of the nut 50. A washerlike member 78 isdisposed between the upper end of the nut 50 and the valve 70, thewasher 78 as well as the valve .70, sleeve 72 and spring 74 beingmaintained in its respective operative position upon suitable tighteningof the nut 50. lt will be seen that when the piston 46 is movedupwardly, fluid under pressure will move downwardly through theapertures 69, thereby unseating the valve 70 and permitting fluid topass into the area below the piston 46, as will be described more fullyin connection with the description of the overall operation of the shockabsorber of the present invcntion.

In accordance with the principles of the present invcntion, the shockabsorber 10 is provided with a new and improved compression valveassembly, generally designated by the numeral 80, which comprises acylinder end member 82, a valve plate 84, a spring disk 86 and one ormore washer-like valve members, generally designated 88. The cylinderend member 82 is formed with a vertically upwardly extending annularside wall portion 90 which defines on the radially inner side therein acentral annular cavity 92. An annular recess 94 is formed around theouter periphery ofthe member 82 and is adapted to receive and be fixedlysecured to the lower end of the pressure cylinder 32. As bestillustrated in FlG. l, the radially outermost lower edge of the member82 is chamfered or tapered, as seen at 95,

and is adapted to be supported upon the upper side of the end cap member20. The cylinder end member 82 is formed with a central annular openingor aperture 96, the upper end of which terminates adjacent an annularvalve seat, generally designated 98, upon which the lower side of thelowermost of the valve members 88 is adapted'to seat or engage, as willbe described.

The valve plate 84 comprises a generally laterally extending bodysection within which a plurality (preferably three) of circumferentiallyspaced apertures 102 are formed. Extending axially upwardly from thecenter of the body section 100 is a generally cylindrically shapedportion 104' which is formed integrally of the section 100 andlocated'equidistant from the apertures 102. Integrally formed on thelower side of the body section 100 of the valve plate 84 and extendingdownwardly therefrom is a generally triangular-shaped portion 106 whichis defined by three substantially equal length sides 108, 110 and 112,which, as best illustrated in FIG. 4, terminate at apex portions 114,116 and 118 that are spaced laterally inwardly from the inner peripheryof the central aperture 96, as best seen in FIGS. 5 and 6. The lowerside of the body section 100 defines a relatively flat, radiallyextending surface 120 against which the upper surface of the uppermostof the valve members 88 is adapted to engage in order to effect afluid-tight seal at the lower ends of the plurality of apertures 102, aswill be described.

The spring disk-86 generallycomprises a ring-shaped or annular supportsection 122, the outer edge of which is substantially the same diameterof the inner diameter of the wall 90 of the end member 82, whereby thedisk 86 may be nestingly received within the upper end of the cavity 92as illustrated. The support section 122 is adapted to be secured to theupper end of the wall 90 by having a reduced thickness portion 124formed at the upper end of the wall 90 crimped or otherwise deformedradially inwardly over the upper surface of the disk portion 122, asillustrated. Extending radially inwardly from and integrally connectedto the ringshaped portion 122 is a plurality of circumferentiallyspaced, radially extending spring fingers, generally designated 126. Thefingers 126, as illustrated in FIG. 3, terminate radially outwardly fromthe center of the member 86 and are adapted to abuttingly engage theouter periphery of the cylindrical portion 104 of the valve plate 84 andthereby operatively support the valve plate 84 for limited vertical orlongitudinal movement with respect to the cylinder end member 82, suchlimited relative movement of the valve plate 84 with respect tothe'member 82 being shown by the respective positions of the valve plate84 in FIGS. 5 and 6.

Each of the valve members 88 is of a generally flat ring-shapedconfiguration and defines a central annular bore or opening 128, withthe diameter of the openings 128 of the valve members 88 being selectedsuch that said members 88 may move relatively free longitudinally of thetriangular-shaped portion 106 of the valve plate 84, yet permit the apexportions 114-118 to prevent any excessive relative lateral or radialmovement of the valve members 88 with respect to the valve plate 84.That is, the valve plate portion 106 functions to guide the valvemembers 88 for relatively free longitudinal movement with respectthereto so as to assure that the members 88 are free to move toward andaway from sealing engagement with respect to the surface 120 at thelower ends of the apertures 102.

In operation, the shock absorber assembly is adapted to-function,generally, in the usual manner, with upward movement of the piston 46directing fluid through the apertures 69, past the valve 70 and into thelower portion of the pressure cylinder 32. Upon downward movement of thepiston rod 30, the fluid in the lower portion of the pressure cylinder32 will pass upwardly through the plurality of apertures 52 and past thevalve 58 into the upper portion of the cylinder 32. The plurality ofvalve members 88, together with the valve plate 84 and spring disk 86normally assume the position shown in FIGS. 1 and 2, wherein the uppersurface of the uppermost of the valve members 88 bears against thesurface 120 of the valve plate 84 and the lower surface of the lowermostof the valve members 88 engages the valve seat 98, thereby blockingfluid flow between the interior of the pressure cylinder 32 and thefluid reservoir 26. When additional fluid is required to fill the areabelow the piston 46, because of the differential in the volume of thecylinder 32 above and below the piston 46, the entire assemblageconsisting of the valve plate 84 and plurality of valve members 88 willmove from the position shown in FIG. 2 to the position shown in FIG. 6,wherein fluid may flow from the reservoir 26 upwardly through theaperture 96, between the lower surface of the lowermost valve member 88and the valve seat 98, then through the interior of the cavity 92, andfinally into the interior of the lower end of the pressure cylinder 32,as indicated by the arrow 130 in FIG. 6. It will be noted that as thevalve plate 84 moves upwardly through the action of the spring fingers126 of the spring disk 86, the plurality of valve members 88 remainpositively engaged with the valve plate 84, that is, the upper surfaceof the uppermost valve member 88 remains contiguously engaged with thesurface 120 so as to block fluid flow through the apertures 102.

Due to the presence of the piston rod 30 within the upper portion of thepressure cylinder 32, pressure will build up within the lower portion ofthe cylinder 32 as the piston 46 moves downwardly. When this occurs, theplurality of valve members 88 will be biased from the position shown inFIG. 2 to the position shown in FIG. 5, wherein the radially innermostportions of the valve members 88 will be biased downwardly or away fromengagement with the surface 120 so that fluid within the lowermost partof the pressure cylinder 32 may pass downwardly through the plurality ofapertures 102, between the surface 120 and the upper surface of theuppermost valve members 88, through the central aperture 96 and back tothe fluid reservoir 26, as indicated by the arrow 132 in FIG. 5.

An important feature of the shock absorber 10 of the present invention,and in particular in the new and improved compression valve assembly 80incorporated therein, resides in the fact that the plurality of valvemembers 88 are not fixed or clamped in any way within the assembly 80,but instead, are free to move longitudinally of the valve plate portion106 and be effectively guided in place by the apex portions 114-118thereof. This arrangement substantially reduces the number of componentparts of the valve assembly 80 to only four thereby reducingmanufacturing costs, as well as minimizing to the extreme, assembly timeand effort required in the production of the valve assembly 80. Anotherfeature of the present invention resides in the fact that thecompression characteristics of the shock absorber 10 may be controlledor determined by the thickness and/or number of the valve members 88,with the result that the compression characteristics may be changedmerely through the addition or substraction of one or more of the valvemembers 88, and/or by varying the effective thickness thereof. This willbe seen to provide a number of advantages from an inventory standpointand greatly enhance the economies of production due to the fact that asingle valve assembly may be produced which may be associated with shockabsorbers of different compression characteristics, with a single valveassembly 80 being universally applicable for each of the shock absorbersmerely through the simple interchanging of valve members ,88.

Referring now to FIGS. 7 through 10, a slightly modified embodiment ofthe compression valve assembly of the present invention is generallydesignated by the numeral 80' and is shown as comprising an annular basemember 82', a plurality of valve disks or members 88, a spring disk 86and a valve plate 84, all of which components are identical inconstruction and operation to the analogous components of the valveassembly 80 designated by like numerals, with the exception of the valveplate 84' which differs from the aforedescribed in the valve plate 84 inthe below described manner. For purposes of conciseness of description,the corresponding components and component parts of the compressionvalve assembly 80 illustrated in FIGS. 7 through 10 which are analogousto identical components or component parts of the above described valveassembly 80, will be designated byv like numerals with a prime suffix.

As best illustrated in FIG. 7, the valveplate 84' comprises a centralbody section having a centrally located upwardly extending section 104'and a generally triangular shaped downwardly extending section 106.

v The underside of the body section 100' comprises a generally radiallyoutwardly extending surface the inner periphery of which is formed withan axially downwardly displaced shoulder portion that defines a flatgenerally radially extending lower surface 152 providing a valve seatextending around the outer periphery of the valve plate portion 106'.The outer periphery of the surface 120' is formed with a seconddownwardly extending shoulder portion 154 which extends around theperiphery of the valve plate 84' and defines a generally flat, radiallyextending surface 156. As illustrated, the surface 156 lies in a planeextending transversely of the axis of the valve assembly 80' that isspaced axially above the plane in which the surface 152 resides. In apreferred construction of the present invention, the surface 156 is inthe order of nine onethousandths (0.009) above the surface 152, forpurposes hereinafter to be described.

As best illustrated in FIG. 10, the shoulder I54 projecting downwardlyaround the periphery of the valve plate 84' is formed with a pluralityof radially inwardly extending, circumferentially spaced recesses ornotches, generally designated by the numeral 158, which function tocommunicate the lower end of the associated pressure cylinder with anannular chamber that is defined by the shoulder portions 150, 154 andsurface 120'. Preferably the notches 158 extend upwardly through theentire thickness of the shoulder 154 so that the upper marginal portionsthereof are generally coplanar of the surface 120'.

As best seen in FIG. 7, the spring fingers 126 of the spring disk 86'are adapted to exert a slight downwardly directed force upon the valveplate 84' and thereby effect a preloading of the valve assembly 80',with the result that the members 88' assume a generally frusto-conicalconfiguration which, together with the axial spacing between thesurfaces 152, 156, results in the upper side of the uppermost of thevalve members 88' being normally spaced somewhat below the surface 156of the shoulder 154, as illustrated.

The operation of the modified compression valve assembly 80 of thepresent invention is substantially identical to the operation of theaforedescribed assembly 80, with the exception that the fluid flowbetween the interior of the associated pressure cylinder and fluidreservoir occurs, in part, through the plurality of notches 158 asopposed to the apertures 102. More particularly, upon downward movementof the associated piston and piston rod, fluid in the lower end of thepressure cylinder will pass through the plurality of notches 158 and tothe chamber 160. By virtue of the fact that the inner peripheral portionof the uppermost of the valve members 88' is engaged with the surface152, fluid flow is prevented between the chamber 160 and the associatedfluid reservoir. At such time as the fluid pressure within the lower endof the pressure cylinder increases to a preselected level due todownward movement of the associated piston and piston rod, the valvemembers 88' will be biased from the position shown in FIG. 7 to theposition shown in FIG. 8, wherein the radially innermost portions of thevalve members 88' are biased downwardly or away from the surface 152 sothat fluid may pass downwardly through the central aperture 96' andintothe associated fluid reservoir. When additional fluid is required tofill the volume within the pressure cylinder, the entire assemblageconsisting of the valve plate 84 and plurality of valve members 88' willmove from the normal position shown in FIG. 7 (or from the positionshown in FIG. 8), to the position shown in FIG. 9, wherein fluid mayflow from the reservoir upwardly through the aperture 96, between thelower surface of the lowermost valve member 88' and the valve seat 98,and finally into the pressure cylinder.

A particular feature of the above described construction resides in thefact that the restriction to fluid flow through the plurality of notches158 may be varied or controlled without altering the effective area ofthe fluid which acts against the upper side of the uppermost valvemember 88' to bias the members 88' from the position shown in FIG. 7 tothat shown in FIG. 8. This is important since it is highly desirable tocarefully control the restriction provided by the notches 158, i.e., bychanging the number or size of the notches, in order to carefullycontrol the operational characteristics of the assembly; however, it isimportant that the area of the uppermost valve member 88 against whichthe fluid acts to effect opening of the members 88' not be changedappreciably upon varying the restriction to fluid flow.

While it will be apparent that the preferred embodiments illustratedherein are well calculated to fulfill the objects above stated, it willbe appreciated that the present invention is susceptible tomodification, variation and change without departing from the scope ofthe invention.

I claim:

1. In combination in a shock absorber,

a pressure cylinder,

a piston movable within said cylinder,

valve means on said piston for controlling the flow of fluid throughsaid piston between the opposite sides thereof,

a reservior,

a compression valve assembly for communicating fluid betwen saidreservoir and said cylinder,

said compression valve assembly comprising an annular base memberdisposed at the lower end of said pressure cylinder and defining acentrally located flow passage and an upwardly projecting ci'rcularvalve seat circumjacent said passage, an annular valve plate arrangedcoaxially of said base member and having a central section extendingdownwardly toward said passage and a radially outwardly projectingsection disposed above said valve seat being formed with a pair ofradially spaced, concentrically oriented shoulder portions defining anannular chamber therebetween, plurality of radially extending,circumferentially spaced recesses formed in the radially outermost ofsaid shoulder portions providing flow paths communicating the lower endof said cylinder with said chamber, and v g at least one generally flat,ring-shaped valve element interposed between the upper side of said basemember and the lower side of said radially outwardly projecting sectionof said valve plate,

the lowermost portion of the radially innermost of said shoulders lyingin a first radial plane and the lowermost portion of the radiallyoutermost of said shoulders lying in a second radial plane spacedslightly above said first radial plane, whereby the upper side of saidvalve element is normally engaged with said radially innermost shoulderand is spaced below said radially outermost shoulder, with the lowerside of said valve element normally being engaged with said valve seat,whereupon a predetermined increase in flu'id pressure within the lowerend of said cylinder results in said valve plate moving downwardly to aposition wherein said lowermost portion of said outermost shoulder isengaged with the upper side of said valve element to slightly deform andeffect a prestressing of said valve element, with a further increase influid pressure in said cylinder resulting in the inner peripheralportion of said valve element being biased downwardly away fromengagement with said innermost shoulder to permit fluid to flow fromsaid chamber through said flow passage into said reservoir, and

upon upward movement of said piston within said cylinder, said valveplate and valve element will move upwardly relative to said base member,re-- sulting in the lower side of said valve element being disengagedfrom said valve seat to permit fluid to flow from said reservoir throughsaid flow passage and around the outer periphery of said valve elementand said valve plate into said cylinder.

2. The invention as set forth in claim 1 which includes spring means inthe form of a plurality of circumferentially spaced spring fingerssecured at their outer ends to said base member and exerting a resilientdownwardly directed force against said valve plate.

tending guide portion means for centrally orienting said valve element.v

6. The invention as set forth in claim 5 wherein said guide portion isof a generally polygonal configuration and which includes at least twooverlying valve elements carried on said guide portion.

1. In combination in a shock absorber, a pressure cylinder, a pistonmovable within said cylinder, valve means on said piston for controllingthe flow of fluid through said piston between the opposite sidesthereof, a reservior, a compression valve assembly for communicatingfluid betwen said reservoir and said cylinder, said compression valveassembly comprising an annular base member disposed at the lower end ofsaid pressure cylinder and defining a centrally located flow passage andan upwardly projecting circular valve seat circumjacent said passage, anannular valve plate arranged coaxially of said base member and having acentral section extending downwardly toward said passage and a radiallyoutwardly projecting section disposed above said valve seat being formedwith a pair of radially spaced, concentrically oriented shoulderportions defining an annular chamber therebetween, a plurality ofradially extending, circumferentially spaced recesses formed in theradially outermost of said shoulder portions providing flow pathscommunicating the lower end of said cylinder with said chamber, and atleast one generally flat, ring-shaped valve element interposed betweenthe upper side of said base member and the lower side of said radiallyoutwardly projecting section of said valve plate, the lowermost portionof the radially innermost of said shoulders lying in a first radialplane and the lowermost portion of the radially outermost of saidshoulders lying in a second radial plane spaced slightly above saidfirst radial plane, whereby the upper side of said valve element isnormally engaged with said radially innermost shoulder and is spacedbelow said radially outermost shoulder, with the lower side of saidvalve element normally being engaged with said valve seat, whereupon apredetermined increase in fluid pressure within the lower end of saidcylinder results in said valve plate moving downwardly to a positionwherein said lowermost portion of said outermost shoulder is engagedwith the upper side of said valve element to slightly deform and effecta prestressing of said valve element, with a further increase in fluidpressure in said cylinder resulting in the inner peripheral portion ofsaid valve element being biased downwardly away from engagement withsaid innermost shoulder to permit fluid to flow from said chamberthrough said flow passage into said reservoir, and upon upward movementof said piston within said cylinder, said valve plate and valve elementwill move upwardlY relative to said base member, resulting in the lowerside of said valve element being disengaged from said valve seat topermit fluid to flow from said reservoir through said flow passage andaround the outer periphery of said valve element and said valve plateinto said cylinder.
 2. The invention as set forth in claim 1 whichincludes spring means in the form of a plurality of circumferentiallyspaced spring fingers secured at their outer ends to said base memberand exerting a resilient downwardly directed force against said valveplate.
 3. The invention as set forth in claim 1 wherein said secondplane is spaced above said first plane between 0.008 and 0.010 inches.4. The invention as set forth in claim 1 wherein said first plane isspaced below said second plane approximately 0.009 inches.
 5. Theinvention as set forth in claim 1 wherein said valve plate includesgenerally axially downwardly extending guide portion means for centrallyorienting said valve element.
 6. The invention as set forth in claim 5wherein said guide portion is of a generally polygonal configuration andwhich includes at least two overlying valve elements carried on saidguide portion.